The present invention relates to electrical connecting arrangements in general and, more particularly, to an electrical plug which is to be mounted on and electrically connected to a free end portion of an electrical cord and is intended to be inserted into an electrical receptacle.
There are already known various constructions of electrical plugs of the above type. A persistent problem in this field is the possibility that the electrical wires of the cord could become loose from their mountings in the plug and create an electrical shock hazard or poor contact and subsequent overheating. To avoid this problem, many plugs are permanently mounted on the cords, that is, the contact-establishing prongs and the mountings of the cord wires to such prongs are permanently encased in a plug housing which is molded around portions of such prongs and the mountings.
However, in many instances, it is required to attach a plug to a cord in situ, without having to replace the entire cord/plug combination, for instance, after the plug has become damaged or inoperative for any reason. Under these circumstances, it is necessary to have available an electrical plug which is separate from any cord but which can be rather easily assembled with the cord on location and will establish a good electrical connection with the cord electrical conductors and be safe in use.
A potential problem in this area is the relatively high forces which may be applied to the cord during the use thereof, for instance, when the user attempts to remove the plug from the receptacle by pulling on the cord, rather than by engaging the plug housing and pulling on the latter. Even though such a practice has been denounced by the manufacturers of electrical equipment and by various safety agencies, it is still being used and hence this possibility cannot be discounted. When this happens, the cord can be subjected to a force of 30 lbs. or more, and this force attempts to extract the cord from the housing.
Various approaches have been proposed to keep the end portion of the cord in the housing despite the application of such rather high extraction forces to the cord, including various clamping arrangements and even arrangements which penetrate or dig into the cord in the transverse direction thereof to resist the extraction force and thus to keep the cord end portion in position in the interior of the plug housing.
It is also important that the electrical connection between the prongs and the respective electrical conductors of the cord be as good as possible, so as to avoid electric sparks or high resistance at the interface between the prongs and the electrical conductors, with attendant danger of damage to the electrical plug. For this reason, it has already been proposed to use piercing or penetrating elements which are in many instances of one piece with the respective prongs and which penetrate into the electrical conductors either transversely of the cord, through the insulating jacket portions of the latter, or from the free end of the cord, substantially in the longitudinal direction of the cord. Obviously, the end penetrating elements have no retaining capability for the cord, but do make better electrical contact. The side penetrating elements do a better job of retaining the cord in the plug housing, since they are so configurated, consistently with their function, as to achieve the best hold but make poorer electrical contact. Because of this, the side penetrating elements usually do possess sufficient retaining capability to maintain the cord in the plug housing, but do not make adequate electrical contact, especially after a long duration of current cycling.